Prior to this invention various types of safety locking devices have been proposed for protecting against accidental disconnection of the male and female coupling members. Representative teachings of such safety locking devices are found in U.S. Pat. No. 3,124,374 issued on Mar. 10, 1964; U.S. Pat. No. 3,976,313 issued on Aug. 24, 1976; U.S. Pat. No. 2,419,916 issued on Apr. 29, 1947; U.S. Pat. No. 2,2023,263 issued on Dec. 3, 1935; U.S. Pat. No. 3,439,942 issued on Apr. 22, 1969; and U.S. Pat. No. 965,998 issued on Aug. 2, 1910.
In prior coupling constructions of the type described in U.S. Pat. No. 2,023,263 vibrations tend to have the effect of dislodging the locking member from its locking position, thereby subjecting the coupling members to accidental disconnection. Other prior coupling locking devices are disadvantageous because they cannot be applied to existing couplings without making significant modification to the coupling structure itself. Still other safety locking constructions of the type described in U.S. Pat. No. 3,976,313, while being less subject to vibrations and adaptable to existing couplings, constitute relatively expensive constructions requiring detent balls and structure for supporting the detent balls in their operative positions. Furthermore, the type of locking device described in U.S. Pat. No. 3,976,313 is non-positive in the sense that it can be released merely by lifting the coupling's latching levers to their disconnect positions.
The present invention, in representing an improvement over the construction described in U.S. Pat. No. 3,976,313, has none of the foregoing drawbacks and offers additional advantages as will become apparent from the following summary and detailed description.